Recent research in the area of social development has focused on the multiple factors that may he involved in the development of socially competent and incompetent behavior. A model of the development of these kinds of early social tendencies has been proposed (Calkins, 1994). This model hypothesizes that early social behavior may be a function of developing emotion regulation skills and strategies, which are, in turn a product of transactions among early behavioral tendencies and maternal caregiving practices. The present investigation will use this model to study the development of early aggressive, impulsive, and hyperactive tendencies that may lead to problematic behavior throughout childhood. A number of studies have attempted to identify the precipitating factors involved in the development of aggressive, impulsive, acting-out behavior problems in childhood. These studies indicate that the etiology of such problems is likely quite complex, and that the problems themselves develop very early in life. However, few studies have examined this development from infancy or considered the multiple behavioral, physiological, and environmental factors that may play a role in the development of these problems.These factors may interact in various ways to produce particular types of social behavior and behavior problems in early childhood. To investigate the relations between these precipitating factors and the development of externalizing behavior problems, a longitudinal study is proposed. The aim of the study will be to select a group of infants who display extreme anger and frustration at 6 months of age, and follow these infants until age 4. The infants will be observed in the laboratory at 6-, 12-, and 18- months-of-age in a series of procedures designed to elicit the child's tendency to display anger/frustration and their strategy for coping with this affect. Physiological reactivity and regulation will also be assessed using measures of heart rate variability (V). At 3O-months- of-age, the infants will be observed in tasks to elicit impulsivity, non-compliance and conflict initiation with peers. Finally, at 4 years of age, peer-directed aggression, social competence and conflict behavior will be observed. The study will examine the interrelations among temperamental, physiological, environmental and regulatory factors to identify pathways to externalizing behavior in preschool.